1. Title: Lesson 5 Alcohols
Learning Objectives:
Explain the relative ease of combustion of the alcohols
Describe the oxidation reactions of the alcohols
Investigate the oxidation reactions of the alcohols

2. Refresh
Which products can be potentially obtained from crude oil and are economically important?
Plastics
Margarine
Motor fuel
I and II only
I and III only
II and III only
I, II and III
Reviewing Your Notes
You should spend 60 seconds reviewing your notes from last lesson before attempting this.

3. Alcohols General structure CnH2n+1OH -OH Functional group
The –OH group is polar  increased solubility in water compared to alkanes of comparable molar mass
Alcohols are used as fuels:
As a fuel for cars – either pure or blended with petrol
Methanol as fuel for competitive motorsports including dragsters and monster trucks
TOK: A large amount of ethanol is fermented from crops…crops that could otherwise be eaten, forcing up food prices. Is this ok?

4. Alcohols as Fuels
Alcohols combust more readily than equivalent alkanes but release less energy since they are already partially oxidised
Alcohol + oxygen  carbon dioxide + water (+ lots of energy!)
Amount of energy released per mole increases as we go up the homologous series, due to increasing numbers of carbon dioxide molecules produced
As with hydrocarbons, in limited supply of oxygen, alcohols will produce carbon monoxide instead of carbon dioxide

5. Oxidation of alcohols
It is possible for them to react with oxidising agents, which selectively oxidise the carbon atom attached to the –OH group, keeping the carbon skeleton intact
A range of compounds will oxidise them so the oxidiser is often represented as [O]
One oxidising agent you need to know is potassium dichromate, K2Cr2O7.
When using this, orange Cr (VI) is reduced to green Cr (III)
Reread the chapter 9 redox for a reminder of how this works
The oxidation reactions of the different alcohols are as follows:

6. Primary alcohols Oxidised in a two step reaction
If you leave a bottle of wine exposed to air, bacteria slowly oxidise the ethanol to ethanoic acid… Giving that smell of vinegar!
Oxidised in a two step reaction
First forming the aldehyde
Oxidised further to the carboxylic acid
It is possible to stop the reaction after the first step using distillation to remove the aldehyde (which has a lower boiling point than ethanol or ethanoic acid) before it oxidises further.
Lower boiling point is because it has no hydrogen bonding.
You can also ensure you get ethanoic acid by using reflux to prolong the contact of the aldehyde with the oxidising agent.
Primary = Carbon attached to one functional group and at least two hydrogens!

7. Distillation v. Reflux heating
Introduction to Reflux Video

8. Secondary alcohols Oxidised to ketones by a similar process:
Secondary = Carbon attached to one functional group, one hydrogens and two alkyl groups!
Secondary alcohols
Oxidised to ketones by a similar process:

9. Tertiary alcohols Not readily oxidised under comparable conditions
Tertiary = Carbon attached to one functional group and three alkyl groups!
Tertiary alcohols
Not readily oxidised under comparable conditions
This would break the carbon skeleton
This would require significantly more energy

10. Summary of oxidation of alcohols

11. Summary of Oxidation reaction scheme

12. Esterification of alcohols
Alcohols react with carboxylic acids to form esters in a condensation reaction
Water is also produced
E.g. reaction between ethanoic acid and ethanol:
The ester has the lowest boiling point so can be separated by distillation
Ester have no free –OH groups so cannot form hydrogen bonds and are mostly insoluble in water
Other examples:

13. Oxidising alcohols
Complete the following investigation into the oxidation of alcohols
Instructions here

14. Key Points Alcohols are highly combustible
Primary alcohols oxidise to form aldehydes, which oxidise to form carboxylic acids
Secondary alcohols oxidise to form ketones
Tertiary do not oxidise due to the 3 strong C-C bonds surrounding the –OH carbon